1. Field of the Invention
The present invention relates to an operation method and an operation apparatus for multi-system refrigerators, and a refrigerating apparatus. In particular, the present invention relates to an operation method and an operation apparatus for multi-system refrigerators for supplying multiple refrigerators with gas compressed by one or more compressors through valves provided for the individual refrigerators. The present invention also relates to a refrigerating apparatus using these operation method and apparatus.
2. Description of the Related Art
A Gifford-McMahon (GM) refrigerator and a pulse tube refrigerator are known as a refrigerator for using a phase difference between a pressure change and a volume change of an operating gas to generate a very low temperature. When refrigerators of this type are provided at multiple locations on a large apparatus such as sputtering apparatus for a semiconductor manufacturing apparatus, a single compressor 10 is shared by a plurality of refrigerators (three in this drawing) 31, 32, and 33 as shown in FIG. 1, instead of providing multiple compressors generating a high pressure and a low pressure for the individual refrigerators to reduce the cost and the energy consumption. In this case, valves 21, 22, and 23 (such as rotary valves) are provided for the individual refrigerators 31, 32, and 33 to supply the refrigerators 31, 32, and 33 with gas (such as helium gas) which is compressed by the single compressor 10, and is supplied alternately through a high pressure line 12 at a high pressure, and a low pressure line 14 at a low pressure.
The refrigerators 31, 32, and 33 conduct a refrigerating process, thereby repeating an adiabatic expansion for generating a low temperature state, resulting in refrigerating first refrigerating stages 31B, 32B, and 33B of cylinders 31A, 32A, and 33A to 30 to 100 K, and refrigerating second refrigerating stages 31C, 32C, and 33C to 4 to 20 K.
In the drawing, motors 41, 42, and 43 drive the valves 21, 22, and 23 to respectively rotate. A power supply line 50 for driving refrigerators provides the motors 41, 42, and 43 with the same drive signal.
However, when the single compressor 10 is used to drive multiple refrigerators 31, 32, and 33, a difference is generated in refrigerating performance of the individual refrigerators 31, 32, and 33 among one another. This is because the timings of the valves for supplying the helium gas in the individual refrigerators 31, 32, and 33 are fixed when the power supply is turned on. As a result, when intake timings overlap one another, more gas flows to the refrigerator which takes in gas first, thereby generating such a phenomenon as an imbalance in gas quantity flown to the individual refrigerators. Thus, when a valve opens in one refrigerator immediately after another valve opens in the other refrigerator, the helium gas is hardly supplied for this valve due to decrease of the supplied gas pressure, thereby presenting insufficient cooling performance. In addition, the helium gas flowing into a more cooled refrigerator is cooled further, thereby having a larger density. As a result, additional helium gas is supplied, thereby cooling this low-temperature refrigerator even further. On the other hand, since the helium gas hardly flows to a less cooled refrigerator, the refrigerator is not cooled sufficiently.
To solve this problem, Japanese Patent Laid-Open Publication Nos. Hei. 3(1991)-15677 and Hei. 4(1992)-272486 disclose such a control method as observing valve timing of the individual valves to feed back the valve timing, thereby controlling the timings for opening/closing are at an equal interval to one another.
However, since it is necessary to observe the valve timing by, for example, detecting currents supplied for the motors 41, 42, and 43 for driving the valves 21, 22, and 23, the complexity of the system increases, resulting in increasing the cost.
The present invention was devised to solve the conventional problem described above, and has an object of providing a simple constitution for solving the imbalance of the cooling performance among refrigerators without observing valve opening/closing timing.
An operation method for multi-system refrigerators of the present invention supplies a plurality of refrigerators with gas compressed by a single compressor through valves provided for the respective refrigerators. This method solves the problem above by shifting an opening/closing frequency of each of the valves slightly to one another.
In this method, a shift amount of the opening/closing frequencies of the valves may be changed depending on the number of the refrigerators. For example, the shift amount is decreased as the number of the refrigerators increases.
An operation apparatus for multi-system refrigerators of the present invention supplies a plurality of refrigerators with gas compressed by a single compressor through valves provided for the respective refrigerators. This operation apparatus solves the problem above by including inverters for slightly shifting an opening/closing frequency of each of the valves to one another.
The present invention also provides a refrigerating apparatus including the operation apparatus described above.
Further, in the present invention, the refrigerators described above may be used as cryopumps, thereby resolving an imbalance in performance among the cryopumps.
With the present invention, it is possible to prevent an overlap of the valve timing with a very simple and inexpensive constitution without means for observing the valve timing, thereby balancing the performance among refrigerators.